Thermal imaging is a traditional technique for thermal management, failure analysis and reliability studies of semiconductor devices (see for example, G. C. Albright, J. A. Stump, J. D. McDonald, H. Kaplan, “True” Temperature Measurements on Microscopic Semiconductor Targets”, SPIE Conference on Thermosense (SPIE Vol. 3700) 1999). However, limitations occur in thermal sensitivity, especially in the face of complex backgrounds and the need to exercise complex circuit structures in order to stimulate the desired site within a device.
Enhanced signal-acquisition techniques, such as binary sampling or quadrature sampling (e.g., Lock-in Thermography S. Kiefer, et al., “Infrared Microthermography for Integrated Circuit Fault Location; Sensitivity and Limitations”, Proceedings of the 28th International Symposium for Testing and Failure Analysis (ISTFA) 2002) that rely on modulating a power supply have extended basic hotspot detection for failure analysis to extremes of sensitivity and show some ability to determine defective depth in simple structures (C. Schmidt, F. Altmann, “Non-Destructive Defect Depth Determination at Fully Packaged and Stacked Die Devices using Lock-in Thermography”, 17th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), 2010).
Binary signal enhancement techniques have been commercially available for many years. Simple binary pulse modulation consists of a single image sample being obtained at each power-on and power-off state, using a synchronously pulse-modulated power supply that is connected to the semiconductor device under test (DUT). This pair of images is digitally subtracted to produce a differenced image in which the common background is removed and only the thermal difference between the on and off power states remains. Averaging multiple pairs of signal samples over tens of minutes allows detection of shorts that are dissipating only a few microwatts.
Recent efforts have focused on quadrature sampling in which two images are taken during the device's power-on state and two during the power-off state. The four images are then combined to produce in-phase and out-of-phase images. An inverse tangent of their ratio produces an additional phase angle image.
These pulse sampling thermography (PST) techniques, described above, have been used for a variety of failure localization applications on static failures. However, there are many dynamic thermal issues in either failure analysis or reliability that require the DUT to be fully on and then placed into a specific state in order for the issue to be become manifest. Desirable thermal measurements are not currently realized.